Their evaluations of the limb joints and feather orientation indicate that a tandem wing design would neither have achieved suitable lift, nor enabled Microraptor to walk on the ground easily.

Instead, the scientists report that its hind legs were positioned below the body, in a bi-plane fashion.

Dr Chatterjee, from Texas Tech University in Lubbock, US, explained that two lines of evidence had led the team to this conclusion.

Firstly, the researchers argue, dinosaurs and birds move their legs in a vertical plane, not sideways as the tandem flight pattern requires.

Secondly, the feathers on Microraptor's hind legs are asymmetrical; one of the two vanes that extend either side of the shaft is narrower than the other.

Forward facing

Aerodynamically, the narrow leading edge of these feathers should face forward in flight, against the direction of airflow. This would have given the flying reptiles lift.

In the tandem pattern, these would have faced sideways.

"We had no other choice but to go for the bi-plane configuration," Dr Chatterjee told BBC News.

A computer flight simulation using this design showed that Microraptor would undulate up and down, an ideal approach for gliding between trees.

The research might also shed light on a contentious debate over the evolution of bird flight.

Some researchers argue that this evolutionary development occurred from the ground up. Others contend that small, feathered dinosaurs were already living in treetops and developed flight in order to get from one tree to another.

This "trees down" model is the one favoured by Chatterjee and Templin.

Alternatively, the bi-plane-like phase could just represent a failed evolutionary experiment.

The Wright stuff

If one accepted the evolutionary importance of the bi-plane formation, there were striking parallels between bird flight and the development of aircraft, said Dr Chatterjee.

Archaeopteryx, regarded as the earliest fossil bird, has what could be described as a monoplane design.

The shift from a bi-plane to a monoplane design could have been facilitated by a much broader wingspan which would have provided increased lift. This mirrors historical developments in aviation.

"We see that the Wright brothers came up with a design for which there was no precedent in nature at the time," said Dr Chatterjee.

"This shows us that if there is a problem in engineering, sometimes there are only one or two possible solutions."